CO-31 Denial Code: Patient Cannot Be Identified as Insured
Payers identify members by a combination of member ID, name, and date of birth. If any of these do not match their records, the claim cannot be tied to a policy and denies with CARC 31. Subscriber and dependent details are a frequent source of mismatches.
Also appears as PR-31. The group code changes who is responsible, not the reason.
CO-31 means the payer could not match the patient on the claim to one of its members. It is almost always a demographic or ID mismatch: a typo in the member ID, a name that does not match the card, or a wrong date of birth. Verify the details against the card and eligibility response, correct them, and resubmit.
Common causes of CO-31.
- Member ID typed incorrectly or taken from an old card
- Patient name spelled differently from the insurance card (nicknames, hyphenated names, suffixes)
- Wrong date of birth, or subscriber and dependent details swapped
- Missing prefix on a member ID where the payer requires it
- Using an outdated Medicare identifier instead of the current MBI
How to work a CO-31 denial.
The order matters: confirm the facts before deciding between a corrected claim, a reconsideration, or an adjustment.
- 1Run eligibility using the exact information from the current insurance card.
- 2Correct the patient and subscriber demographics in your practice management system.
- 3Resubmit the claim with the corrected information.
- 4Check other open claims for the same patient, which likely carry the same error.
How to keep CO-31 from coming back.
- Scan front and back of insurance cards at every visit
- Run eligibility before the appointment and correct mismatches immediately
- Enter names exactly as shown on the card
Fixing this at the source usually sits with eligibility verification →
Questions about CO-31.
Denials that often travel with this one.
CO-27: Expenses Incurred After Coverage Terminated
CO-27 (often PR-27) means coverage was not active on the date of service. How to verify eligibility, find new coverage, and bill correctly before timely filing.
Read about CO-27 →CO-16: Claim Lacks Information or Has Billing Errors
CO-16 means the claim is missing information or has a billing error. How to use the RARC to find what is missing, correct it, and stop it from recurring.
Read about CO-16 →CO-22: Care May Be Covered by Another Payer
CO-22 (often OA-22) means the payer believes another plan is primary under coordination of benefits. How to confirm coverage order and get the claim paid.
Read about CO-22 →Add a Dedicated Denial Specialist
RCM Staff places trained denial management specialists inside your EHR and clearinghouse to work the queue, correct and appeal claims, and track root causes by payer.
Kevin Jamito has 18+ years of U.S. healthcare revenue cycle management experience across billing, coding, practice management, and offshore RCM operations. He founded RCM Staff to give U.S. healthcare teams dedicated Philippines-based specialists who work inside their existing systems.